The conventional process for manufacturing polyamides is known as the "salt-strike" process. In this process, aliphatic dicarboxylic acid monomer is admixed with aliphatic diamine monomer in aqueous solution to form a salt. The salt is fed into a reactor in which both temperature and pressure are elevated. With the emission of water and volatile matter, molten polymer is formed and discharged from the reactor.
Alternative routes to the manufacture of polyamides have been developed. For example, processes in which a dinitrile and a diamine are polymerized to form linear polyamide are described in a number of patent references such as U.S. Pat. No. 2.245,129 to Greenwalt, U.S. Pat. No. 3,847,876 to Onsager, U.S. Pat. No. 4,436,895 to Hoffman et al., and U.S. Pat. No. 4,520,190 to Coffey et. al.
More recently, U.S. Pat. No. 4,739,035 to Shyu et al., describes a two-step process for the manufacture of a polyamide from diamine and dinitrile reactants in which the dinitrile is initially reacted with water in the presence of a catalyst at a temperature sufficient to cause substantial hydrolysis of the dinitrile. Subsequently, the diamine is added to the reaction mixture at a temperature sufficient to cause polymerization.
In a further U.S. Patent, U.S. Pat. No. 5,109,104 to Marks, a process for making polyamide is taught in which an omega-aminonitrile is heated with water and an oxygenated phosphorus catalyst at a pressure of between 200-350 psig. Upon reaching a temperature of 200.degree. C.-260.degree. C., water is added continuously, to a total amount of 15-75 grams/100 grams of omega-aminonitrile, and once the temperature is above 240.degree. C., water vapor and ammonia are continuously removed from the reactor. The resultant mixture is then polymerized at a temperature between 240.degree. C.-330.degree. C.
There are, however, disadvantages associated with the processes described above. Firstly, processes in which dintrile and diamine monomers are reacted tend to yield lower molecular weight polymers due to incomplete hydrolysis of the dinitrile functionality. Moreover, these processes can lead to the formation of organic by-products which causes discoloration of the polymer product. In the manufacture of branched polymers, these problems are accentuated in the polymer product. Alkyl branched monomers are generally more volatile than their linear counterparts and this makes them more prone to by-product formation. As a result, problems of lower molecular and discoloration in the polymer product are enhanced. Accordingly, there is a need for improved methodology, particularly in the manufacture of branched polyamides.